Electrolytic production of elemental boron



Patented Oct. 23, 1951 o'rRoLrTio PRODUCTION 0.1? E EMENF BQBON Hugh S.Cooper, Shaker Heights, Ohio, assignor No Drawing. Application June1,1950,

- Serial No. 169,529

21 Claims.

This invention relates to electro-metallury and I particularly to anelectrolytic method of-producings'ubstantially pure elemental boronandto the resulting product. The principal object of the invention is toprovide; a method, for producing substantially pure elemental boron on acommercial scale.

Another object of the invention is to provide a method .for producingelemental boron in a form which lends itself readily to melting,pressing, and sintering into various shapes and to diverse uses in the.metallurgical, chemical, and other industrial arts.

A further object of the invention is to produce elemental boron ofsuiificient purity to be suitable fordirect use in the production ofhigh purity Though practically insoluble in acids and almost as hard assilicon carbide, the free el ment been put to no practical use as suchprior to the last decade, and is still used onlyto a very small extent,if at all.

It has previously been discovered that elemental boron has a number ofproperties that make it potentially of great value in many fields. Forexample, its exceptionally high specific re sistance at room temperaturedrops rapidly as the temperature increases, a characteristic that lendsitself to extensive use in various types'of electrical apparatus.

,Mere traces of boron in carbon change the temperature coefficient ofresistance from negative to positive, giving metal-like electricalcharacteristiostothe carbon.

.Boronis a very powerful deoxidizer and has a high affinity for variousgases. This makes it highly useful in metallurgical field's, as a'degassisa ge i d ment a gfei isaqsiifi j d i e- QI IUS al o. graetiqa lveeplet y insoluble inrco pe beinequ te a n ueme a in this respect, and istherefore probably the best agent known for the treatment of moltencopper to remove occluded gases therefrom during the mak esb copp er isea er- Due to their great hardness, free boron metal andboron in theform of alloys andcompunds, such "as metal borides; should also findmany ob- Vi0us"'app1icati0ns' in 'industry when the free metal isavailable in commercial'quantities.

While it is said that boron oxide" (B203) may bereduced by-heating in'the presence of magne siurn to produce magnesium'oxid'e an'dfree'boron', the process generally carriesthe boron only'to what hasbeen -termed-a' suboxide (B 0) When aluminumis employed" in place ofmagnesium, aluminum borid-e (A1312) is the result. Boron chloridehasbeenbroken down by a-high tension arc in the presenceof' hydrogento give thepure element but the yields a-re-loW-and the process is impractical forthe productionof boron-incommeroialduantities. I 7

'Ih'e electrolysis of boron oxide in a fused bath of'magnesium'oxide andmagnesium fluoride has beentried, butbath temperatures of 1100 to 1200 CWBIBTOLllld to be-neces'sary;-and-metal of'only about 92 purity'wasobtained, probably du'e in' part to the high temperature-and tc-thedifliculty of separating the highly insoluble magnesium salts from theproduct.

Boron is a member of Group III of the periodic table, being grouped withaluminum, lanthanum, yttrium, etc., of which only aluminum is producedor used in commercial quantities. None of the prior art processes forproducing any of these othermetals in free form'is, so far as I amaware, at all useful or practical for producing free'boron.

Ingeneral, my process involves the electrolysis of a fused bath ofpotassium chloride or fluoride, potassium fluoborate, and boron oxide(B203). While processeshave heretofore been employed to produceso-called refractory metals falling in other groups of the periodictable by electrolysis of their double fluoride salts, their oxides, etc,the same processes; when applied to the electrolysis 'of similar saltsand oxides of 'boron, have either failed to operate at all-for theirintended purpose, have yielded a product tooimpure for practicaluse,orhave involved such serious operating difficulties as to be entirelyimpractical as commercial processes. Such prior artproce'sses,therefore, instead of pointing the way to the as. complishm'ent'oftheforegoing objectives, have actually's'er'ved' asmisleading sign postsdirecting theart away'fro'm attempts to'produc'e boron bytheelectrolysis' of the aforementioned types of;

jfn accordance with the present invention, 1 have found that elementalbdron' in" thefo'rm of substantially pure fine crystals can beefficiently produced by electrolyzing a fused bath of potassium chlorideor fluoride, potassium fiuoborate, and boron oxide at temperatures inthe range of about 650 to about 1000 C., the boron being deposited onthe cathode of the electrolytic cell in its fine granular form, togetherwith predominantly water and acid soluble impurities, and being readilyremovable from the cathode and purified by Washing.

An electrolytic cell for use in the process of this invention mayinclude an externally heated crucible of graphite or similarelectrically conductive refractory material protected by an outer shellof a high heat resistant metal, such as the nickel, chromium, and ironalloy marketed under the name Inconel. If desired, heating of thecontents of the crucible may be carried out by electrical induction orby electrical resistance heating in the bath itself. The crucible formsthe anode of the cell and the alloy Shel]. may be connected to thepositive terminal of a source of direct current. Alternatively, the leadfrom the positive terminal of the source of direct current may beconnected directly to the graphite crucible itself. Molybdenum orInconel sheets or plates are suitable for the cathode when operating ona relatively small scale. However, in large scale operations involvingcathode plates ranging upwards in size from 8 inches wide by 16 incheslong, with plate thicknesses of /1 to /2 inch or more, the use of thesemetals for the cathode presents a number of difficulties.

Molybdenum cathodes, alter use in a large cell on a continuous basis fora period of time, become brittle and tend to flake oil and contaminatethe product. While the molybdenum shows little tendency to combine oralloy with boron, removal of the molybdenum from the product isdifiicult because of its low solubility in acids. Also it is difficultto obtain molybdenum in large enough sheets of sufiicient thickness, andsuch sheets are unreasonably expensive when obtainable.

Inconel cathodes, when used in large cells on a continuous orsemi-continuous basis, have been found to produce excessive nickelcontamination of the product, forming acid-insoluble nickel borides thatare practically impossible to separate by chemical means from theelemental boron.

While copper cathodes have been used in many electrolytic processes, Ihave found this metal to be quite unsuitable for use in carrying out theprocess of the present invention. The surface oxidation of copper has atendency to contaminate the bath or the product unduly and tends to peeloff with the product when the cathodes are stripped.

In an eifort to find a satisfactory cathode material, low carbon ironwas tried in spite of its reactivity and alloying characteristics. Whencathodes of this material were removed from the cell and quickly coatedwith salt and allowed to cool, the bulk of the boron deposit was foundto strip off easily when tapped with a hammer, but a thin adherentcoating of boron was found remain. By leaving this thin coating on theiron cathode, instead of trying to scrape off all of the boron accordingto prior practice, it was found that iron contamination stayedsurprisingly low, generally being well below 0.5%. This amount of ironmay be largely removed by an acid wash and presents no significantproblem, whereas the contamination resulting from the use of cathodes ofmolybdenum or Inconel is not removable by any commercially practicalprocess.

4 Further advantages of low carbon iron cathodes are their excellentresistance to warping, low cost, and availability in any desired sizesand shapes.

A particularly suitable iron for the cathode, which is availablecommercially, is Armco Iron. This product contains approximately 0.12%carbon, 0.017% manganese, 0.005% phosphorous, 0.025% silicon, and thebalance iron. However, any low carbon and low alloy iron may beemployed. The carbon is preferably kept close to or below 0.1%, ashigher carbon contents appear to promote objectionable warping of thincathode plates.

For a more complete understanding of the present invention and theeffects of varying the raw materials, operating conditions, and types ofapparatus employed, reference will be made to a number of specificexamples. However, it is to be understood that these examples have beenselected merely for illustrative purposes, and that the details thereofmay be changed in many particulars as indicated in the, accompanyingdiscussion.

Example 1 4000 grams of potassium chloride and 1500 grams of potassumfiuoborate were melted together in a graphite crucible of the typedescribed above, measuring 6 inches inside diameter and 8 inches indepth, and the melt was brought to a temperature around 800 C. To thisfused bath was added 500 grams of boron oxide (B203), which quicklydissolved in the bath. A sheet molybdenum cathode about 3% inches wide,'7 inches long, and 0.1 inch thick was then lowered and completelyimmersed in the bath, and the current was turned on to place the cell inoperation. The voltage ranged from 6.3 to 7.8 volts with an averagecurrent of about 580 amperes that remained substantially constantthroughout the run.

During the operation of the cell, elemental boron was deposited on thecathode, and oxygen was released at the anode. A thick black scum formedover the surface of the bath, but the amount of the scum was small, andno eifort was made to identify it or remove it. Electrolysis wascontinued without interruption for about 2 hours, after which thecurrent was shut off. and the cathode was withdrawn and quickly coveredwith dry sodium chloride to protect the boron deposit from oxidation.When the cathode had cooled to below a visible red glow of the materialclinging thereto, the cathode was immersed in water for a period ofseveral hours,

during which time most of the deposit had fallen off and the remainderwas readily scraped off. Upon prolonged digestion of the removed depositwith water, and then with strong hydrochloric acid, the residue wasfinally washed with water, dried, and sifted for size classification.

The product was in the form of fine crystals, about 90% of which passedthrough a 325 mesh 118 grams of the final product were recovered.

Calculated on the basis of 1% of moisture in the 500 grams of boronoxide imltiallyucharged into the crucible, and on the basis of98.6 8% ofthe product being pure boron, thefinal yield repre-. sented about 78% ofthe amount of boronin the initial charge. Since the run was carried outon a batch basis with electrolysis being stopped before detecting anyevolution of chlorine, which would indicate completev exhaustion of the.boron oxide, the recoverypotentialities of the process when operated ona, continuous basis were demonstrated to be unusually high.

Upon attempting to apply the above described process to largeelectrolytic cells, and particularly when operating on a continuousbasis, Ithen dis-P. covered that the purity of the boron drops substantially and that the carbon content may re-. main as high as 3 or 4%.evenafter thorough washing. This is objectionable for manyof themetallurgical uses for elemental boron, and is especially so when usingthe boron to produce metal borides or for various purposes in atomicenergy and radio activity projects. Since the carbon is insoluble in allreagents, its satisfactory removal from the product is practically impossible. Thus, in the many instances in which carbon impurities aredetrimental, mere enlargement of the scale upon which Example 1 wasperformed is not entirely satisfactory, particularly when operating on acontinuous basis. Commercial use of the process, as described in Example1, therefore, should. preferably be confined to relatively smallequipment and batch operation.

As noted in the foregoing: example, a black scum was observed on thesurfaceof thebath during the electrolysis. When employing a larger. cellon a continuous'basis, this scum accummulated in somewhat greateramounts. Examination of the scum in later work disclosed thatitconsisted largely of finely divided carbon, presumably produced by theerosive action of thehot bath on the graphite crucible, the bath beingkept in a constant state of agitation by the high current passingtherethrough. Surprisingly, when this scum was removed at frequentintervals during the electrolysis, sothat its quantity" was preventedfrom buildingup, the-carbon contamination problem wassubstantiallyeliminated. In fact, the amount ofcarboninthe product wasreadily held well below- 0.50 percent while operatingcontinuously, andwas frequently reduced to about 0.15 per cent. More thorough washingsometimes helps in still further reducing the carbon contentof theproduct.

To illustrate the results obtainedby employing the skimming step,reference is made to the following two comparative examples in which'theequipment was basically the same as'that employed in Example 1, thoughsubstantially larger in size.

Example 2' The crucible employed in thisgexample was generallycylindrical in form and was lined on .the sides and the bottom withapproximately three inches of graphite. Theinterior diameter of thecrucible was 10 inches and its vertical height was 13 inches. Thecathode employed was made of iron and was inch thick, 5 inches wide, and9 inches long.-

14 kilograms of potassium chloride-and 4.5 kilograms of potassiumfiuoborate were melted together in the crucible and brought to-atemperatureof about 850 C. To this fused'bath was. added. 1.5ki1ograms'of boron oxide; Thecurrent .was.then applied andelectrolysiswas continued .for 8 hours with an averag :voltage of'about 6.0 and anaverage amperage of about.

500. The black scum appeared as before, but it was allowed to accumulatewithout being' re moved.

At the end of the electrolysis period the oathode was removed, quicklycovered with'dryso' dium chloride, and, after cooling, the cathodedeposit was removed and purified as in Example 1. This purified productamounted to 440 grams,

which was sifted to give 45 grams of material passing a 40 mesh screenand held on a 100 mesh screen, 50 grams of material passing a '100-mesh:

screen and held on a'200 mesh screen, and" 345* grams of material finerthan 200 mesh. Upon."

separate analysis of these three components, thecoarse material wasfound to be only about'81% boron and nearly 5% carbon and was discardedas commercially unusable. The other two components gave the followinganalyses":-

The combination of these last two components represented a boron yieldof'abofut in the formof material containing about 96% boron and about1.4 carbon.

Example '3 In this example, the'same equipment and the;

same bath ingredients and procedure were em ployed as in Example 2,except that theblaclc carbon scum was skimmed the bath every tenorfifteen minutes during the electrolysis. 390 grams of product were-recov-' ered in five hours of operation, represent,-

ing about 86% recovery based on the amount;

of boron in the boron oxide charge material. Of. the 390 grams ofproduct, 335 grams passed through a 325 mesh sieve and the remainder.was made up of particles held on a 40 mesh sieve..- Analysis of theproduct indicated the following;

average composition:

Ber-cent. Boron 99.50; Iron 0.282 Carbon 0.16; Undetermined 0.06

By-a comparison of the carbon contents of the-products of Examples 2 and3, the "impor-' tanceof skimming the black scum from the sur* face ofthe bath is strikingly apparentn While the foregoing run was made with asingle.

chloride, the following example is giveninjwhich' the process wascarried out in the same apparatus employedin Exampleszand 3.

Example; 4

5500 grams of potassium=fiuoride and 2000' from the surface of.

grams of potassium fluoborate were melted together in the crucible andbrought to a temperature'of about 900 C. To this fused bath wasadded;500 grams of boron oxide, which quickly dissolved in the bath. Aniron cathode about 3 /4 inches wide, '7 inches long, and 0.1 inch thickwas immersed in the bath and the current was turned on. The voltageremained close to 6.75

volts and averaged about 725 amperes with very littlefluctuation, thusindicating little or no. anode effect in spite of the high fluoridecontentof thebath. As in theprevious examples, a small quantity of blackscum was observed to accumulate on the surface of the bath and wasremoved every ten to fifteen minutes. Electrolysis was continued for 2hours. 7

About 105 grams of product was recovered from the washing operations andsifted for'size grading, the sifted material beingabout half larger andhalf smaller than 910 mesh, with little or none of the very finematerial of Examples 1, 2, and 3. The finer and coarser portions of theproduct were separately analyzed with the following results:

Fine material Coarse material Per cent Per cent Boron 94.1 Boron 96.7Iron 0.8 Iron 1.0 Carbon 1.2 Carbon 0.6 Undetermined--- 3.9 Undetermined1.7

The total boron recovery was approximately 67%. Though the purity wasnot as high as in the preceding example in which potassium chloride wasemployed as the main bath solvent, rather than potassium fluoride, thedifference is partly attributable to greater impurities in the potassiumfluoride used. However, the lower purity may also have been due in partto the combined effects of the higher bath temperature that had to beemployed to melt the potassium fluoride (m. p. about 800 C.) the highercurrent density, and the consequently greater erosive activity of thebath. The most striking difference in the product resulting from thesubstitution of potassium fluoride for potassium chloride was the greatincrease in the particle size of the product.

Examples 1 to 4 were all carried out strictly on'a batch basis toestablish the general operative character of the process and thepreferred procedures for obtaining a high purity product. While theyields were calculated and noted with interest, no particular effort wasmade to obtain the maximum yield of product per gram of B: chargedmaterial. If batch operation on a commercial basis were to be practiced,it would obviously be desirable to modify the foregoing examples in oneof two ways to obtain optimum yields per gram of boron containing bathingredients. One modification would be to reuse the bath materialsremaining at the end of one batch operation in a second batch operationby adding a new charge of B203, which would be practically the same'asoperating on a continuous basis as far as the ultimate boron yield andcost of bath solvent materials are concerned. The other modificationwould be to continue the electrolysis after the B203 is exhausted, inwhich case the potassium fluoborate in the bath would be consumedtodeposit boron at the cathode, produce additional potassium fluoride inthe bath, and release chlorine at the cathode, all in accordance with myprior copending application, Serial No. 120,414, filed October 8, 1949.H

In that prior application I disclosed and claimed a process forproducing boron by the electrolysis of a fused bath of potassiumchloride and potassium fluoborate in which the fluoborate constitutesthe source of boron, and chlorine is released at the anode as a resultof decomposi tion of the potassium chloride. The potassium from thepotassium chloride decomposition combines with the available fluorinefrom the po-' tassium fluoborate to produce potassium fluoride in thebath at a rate several times equivalent to the amount of chlorine andboron released at the anode and cathode respectively. Continuation ofthe process of the present application after exhaustion of the B20:merely results in con suming the KBFi of the bath in accordance with mycopending application, Serial No. 120,414. The boron so produced fromKBF4 tends toward larger particle sizes, but such larger particles arereadily separated from the smaller particles by screening, which isusually practiced regardless of the percentage of large particle sizespresent in the product. Moreover, it appears that particle size may becontrolled by proper adjustment of the electrolysis process.

This last described continuation of a batch process is practical onlywhen potassium chloride is used as the solvent for the potassiumfluoborate. When potassium fluoride is substituted, continuedelectrolysis after exhaustion of the B203 releases fluorine at theanode, and this causes a number of complications, including pronouncedanode effects.

To illustrate the application of the present invention to continuousoperation in still larger equipment, the following example is given:

Example 5 The crucible employed in this example was generallycylindrical in form and lined on the sides and bottom with approximatelythree inches of graphite. The interior diameter of the crucible was 16inches and its vertical height was 30 inches. The cathode employed wasArmco iron /2 inch thick, 8 inches wide, and 16 inches long. the cathodeplate being suspended from a copper rod having a slotted lower end withthe plate disposed in the slot and bolted in place. The rod was made ofcopper to minimize electrical losses therein resulting from theresistance of the rod and the high current employed. To preventoverheating of the rod, which promotes surface oxidation thereof and thelikelihood of contamination of the bath with copper oxide, the rod wasmade hollow, and cooling water was introduced through a small diametertube disposed in the hollow copper rod with its open end adjacent thebottom thereof. Thus, water issuing from the lower end of the tubeflowed upwardly around the tube and was piped off at the upper end ofthe hollow rod.

The crucible was heated by gas burners for initially melting the solventcomponents of the bath. 225 lbs. of potassium chloride and lbs. ofpotassium fluoborate were melt-ed in the crucible, and the bath wasbrought to a temperature of about 860 C. by means of the gas burners.With the current turned on, boron oxide was added at fifteen minuteintervals in amounts of 4 lbs. at a time until 12 lbs. had been added.Thereafter, additional boron oxide was supplied at intervals of a halfhour or so in 4 lb. increments throughout the run.

Every three to four hours, the cathode was removed for recovery ofboron, the cathode being quickly coated with; sodium chloride upon withdawa 19m therein... RemQva1...or the. deposit v from the cathode wascarried out, as described reinserted for continuing the process.Additional potassium chloride and potassium fluoborate, in the initialratio of 3 to 1, were also added at about three to four hour intervalsto make up for the small amounts lost by vaporization-and theconsiderably larger amounts entrained with the cathode deposit andlostfrom the bath .when the cathode was withdrawn for recovery of borontherefrom. The total potassium chloride added during the run was 135lbs. and the total potassium fluoborate added was '75 lbs.

The run was continued for about '72 hours, exclusive of interruptionsfor removing the cathode deposits, during which time the current wasmaintained very uniformly at 2500 amperes with the voltage varyingslightly between 7 and 8 volts. Then, before concluding the run, thecurrent was raised to 4000 amperes at 10 volts for 2 hours to clean upthe available boron in the bathas completely as possible. The bath wasskimmed about every 15 to 20 minutes throughout the run.

The total amount of boron oxide used during the run was 142 lbs., ofwhich about 42.6 lbs. was

boron. The cathode deposits were washed with water and acid in the usualmanner, and the thus purified product amounted to 38.4 lbs., or about88% recovery of the boron in the boron oxide charge material. Thecurrent efiiciencyfor the entire run was extraordinarily high, beingabout Because of the large amount of the product, it

Pounds of product Per cent boron The batches of highest boron puritywere, of course, also lowest in carbonand iron impurities.

It will be apparent from Example that the process as disclosed thereinis admirably adapted for continuous operation in still larger cellscapable of receiving several cathode plates at a time. In such a case,the cathode plates would preferably be removed one at a time forrecovery of boron, and a, replacement cathode would be immediately orsimultaneously inserted in the bath. This operation could bemechanically performed with a variety of mechanical devices forsuspending the cathodes, as will be readily appreciated by those skilledin the art.

By contrast with the process of my above mentioned copendingapplication, Serial No. 120,414, inwhich KBF4 is employed as the sourceof boron and chlorine is evolved at the anode, the present processemploys boron oxide as the source of boron and oxygen, rather thanchlorine,'is released at the anode. While I do .not wish-to be limitedby any'theory-of operation, it appears-that 1121116 130- vtassiumfluoborate is dissolved in the potassium chloride or potassium fluorideand that the boron oxide is in turn dissolved in the potassiumfluoborate. The alkali compounds are apparently not disassociated by thecurrent, as only boron oxide appears to be consumed.

While the potassium chloride or fluoride and potassium fluoborate in thepresent process remain in the bath unchanged, apparently acting only aselectrically conductive inert vehicles, their presence is essential forthat purpose.

' Without the potassium chloride or fluoride, the

potassium fluoborate would undergo slow thermal decomposition at thebath temperatures and would become viscous and gummy in the presence ofboron oxide alone. Without the potassium fluoborate, the bath is verygummy and unmanageable, and no product is obtained.

The proportions'of potassium chloride or fluoride, potassium fluoborate,and boron oxide employed in the foregoing examples are in no wisecritical, and. substantial variation from these proportions ispermissible, so long as the bath remains homogeneous. Since thepotassium fluoborate is protected from thermal decomposition by beingdissolved in the potassium chloride or fluoride, it is necessary thatthe amount of potas- "sium chloride or fluoride be sufiicient for thatpurpose. In addition, the viscosity of the bath is affected by theproportions of these two ingredients. By keeping the amount offluoborate less than the amount of the chloride or fluoride, the firstcondition is more than satisfied and the bath will have the preferreddegree of fluidity.

The amount of boron oxide is limited by the amount that will easilydissolve in the bath, and this is largely dependent upon the amount ofthe fluoborate, which acts as the solvent for the boron oxide. Theelectrical efiiciency of the process is not noticeably affected untilthe boron oxide is nearly consumed. So long as an appreciable quantityof boron oxide is present, any amount up to the limit of its solubilityin the bath may be employed initially, and additions need only be madesufficiently often to keep the amount of boron oxide within the widelyseparated limits indicated.

In the process of my copending application, Serial No. 120,414, theboron deposited on the cathode is a coarse crystalline aggregate havinga purity of about 99.5%. In the process of the present application, theboron is formed as crystals of considerably smaller particle size andabout the same purity. If the boron oxide in the bath of the presentinvention is not replenished before it becomes exhausted, continuationof the electrolysis results in the deposit of boron from the potassiumfluoborate in accordance with the process of my copending application,as explained above. Because this tends to produce boron crystals ofconsiderably larger size than those resulting from the electrolysis ofthe boron oxide, it may be desirable that the boron oxide in the hathnot be permitted to become exhausted if only the small particle sizeproduct is desired. Also, if potassium fluoride is employed in place ofpotassium chloride in the present invention, a much coarser product isobtained. However, as previously indicated, further experimentation withdifierent rates of deposition, cell sizes, cathode to anode surfaceratios, and bath compositions may give some measure of control ofparticle size in both the present oxide process and the KBF4 process ofmy application Serial No. 120,414.

The process of the present invention is preferable from the standpointof the cost and availability of the material used as a source of boronand also from the standpoint of power consump tion, the latter advantageresulting from the lower resistance of the bath in the process of thepresent invention. Also the maximum current that can be passed throughthe bath of this process with optimum yield per ampere, is from 50% to100% greater for a given cell than when the bath of the process of mycopending application is employed, thus giving a far greater productionrate.

From the standpoint of the cuality of the resulting product, the processof the above mentioned copending application may be preferable forcerain uses because of the larger particle size of the product. In otherinstances, the fine particle size material is preferred. The choicebetween the two processes, therefore, is dependent primarily upon theuses to which the product is to be put.

In the fore oing spe ification my invention has been illustrated byreference to several specific examples, and certain variations thereofthat may be followed in practice have been mentioned in more or lessdetail. It will be appreciated, ho ever, that still other variations ofdetails of the process will occur to those skilled in the art and may bepracticed without departin from t e true spirit and scope of theinvention as defined in the appended claims.

In the claims, the expression normall gaseous halo en is employed todesignate chlorine and fluorine, which are the only halogens that aregases at normal temperature and pressure.

Having disclosed my invention in detail, I claim:

1. The process of preparing boron comprising electrolvzing a fused bathconsisting essentially of a potassium salt of a normally gaseoushalogen, potassium fluoborate, and boron oxide.

2. T e process of pre rin hmnn nmnriei electrolyzin a fused bathconsisting essentially of a potassium salt of a normally gaseoushalogen, potassium fluoborate, and boron oxide in an electrolytic cell,and removing the cathode of the electrolytic cell for recovery of borondeposited thereon.

3. The process of preparing boron comprising preparing a fused mixtureconsisting essentially of a potassium salt of a normally gaseoushalogen, potassium fluoborate, and boron oxide, and electrolyzing saidmixture in an electrolytic cell to deposit boron on the cathode, theamount of said potassium salt being suflicient to dissolve the potassiumfluoborate and maintain the bath in a fluid state.

4. The process of preparing boron comprising preparing a fused mixtureconsisting essentially of a potassium salt of a normally gaseoushalogen, potassium fluoborate, and boron oxide, electrolyzing saidmixture in an electrolytic cell having an iron cathode.

5. The process of preparing boron comprising preparing a fused mixtureconsisting essentialh of potassium chloride. potassium fluoborate, andboron oxide, electrolyzing said mixture in an electrolytic cell whilemaintainin the mixture in the range of about 650 to about l000 0., andremoving the cathode of the electrolytic cell for recovery of borondeposited thereon.

6. The process of preparing boron comprising preparing a fused mixtureconsisting essentially of potassium fluoride, potassium fluoborate, and

, l2 boron oxide, electrolyzing said mixture in an electrolytic cellwhile maintaining the mixture in the range of about 800 to about 1000"C., and removing the cathode of the electrolytic cell for recovery ofboron deposited thereon.

7. The process of preparing boron comprising preparing a fused mixtureconsisting essentially of potassium chloride, potassium fluoborate, and?boron oxide, electrolyzing said mixture in an: electrolytic cell whilemaintaining the mixture in'-- the range from about 650 to about 1000"C., adding boron oxide to the mixture in the course of' the process toreplace that consumed during the electrolysis, and recovering boron fromthe cathode.

8. The process of preparing boron comprisingpreparing a fused mixtureconsisting essentially: of potassium fluoride, potassium fluoborate,andboron oxide, electrolyzing said mixture in an electrolytic cell whilemaintaining the mixture im the range from about 800 to about 1000- C.-,add ing boron oxide to the mixture in the course of the process toreplace that consumed during theelectrolysis, and recovering boron fromthe cathode.

9. The process of preparing boron comprising preparing a fused mixtureconsisting essentially" of potassium chloride, potassium fluoborate,andboron oxide, electrolyzing said mixture in am electrolytic cell todeposit boron on the cathode while maintaining the mixture in the rangefrom; about 650 to about 1000 0., adding boron oxide to the mixtureduring the course of the elec-' trolysis to replace that consumed bydecomposition, recovering boron from the cathode, and purifying therecovered boron by washing with water and acid.

10. The process of preparing boron comprising preparing a fused mixtureconsisting essentially of potassium fluoride, potassium fluoborate, andboron oxide, electrolyzing said mixture in an electrolytic cell todeposit boron on the cathode while maintaining the mixture in the rangefrom about 800 to about 1000 C., adding boron oxide to the mixtureduring the course of the electrolysis to replace that consumed bydecomposition, recovering boron from the cathode, and purifying therecovered boron by washing with Water and acid.

11. The process of preparing boron comprising preparing a fused mixtureconsisting essentially of potassium chloride, potassium fluoborate, andboron oxide, the amount of potassium chloride being at least as great asthe amount of potassium fluoborate, and the amount of potassiumfluoborate being suflicient to dissolve the boron oxide, electrolyzingsaid mixture in an electrolytic cell to deposit boron on the cathode,and removing the cathode from the cell for recovery of boron depositthereon.

12. The process of preparing boron comprising preparing a fused mixtureconsisting essentially of potassium fluoride, potassium fluoborate, andboron oxide, the amount of potassium fluoride being at least as great asthe amount of potassium fluoborate, and the amount of potassiumfluoborate being sufficient to dissolve the boron oxide, electrolyzingsaid mixture in an electrolytic cell to deposit boron on the cathode,and removingthe cathode from the cell for recovery of boron depositthereon.

13. The continuous process of preparing boron comprising preparing afused mixture consisting essentially of potassium chloride, potassiumfluoborate, and. boron oxide, the amount of potassium chloride being atleast as great as the amount of potassium fluoborate, and the amount ofpotassium fluoborate being sufficient to dissolve the boron oxide,electrolyzing said mixture in an electrolytic cell having a removableiron cathode to deposit boron on the cathode while adding boron oxideperiodically to replace that consumed by electrolysis, and removing thecathode from the cell from time to time for recovery of boron therefrom,the recovery of boron from the cathode being performed so as to leave anadherent coating of boron substantially completely covering andprotecting the surface of that part of the cathode immersed in the fusedbath.

14. The continuous process of preparing boron comprising preparing afused mixture consisting essentially of potassium fluoride, potassiumfluoborate, and boron oxide, the amount of potassium fluoride being atleast as great as the amount of potassium fluoborate, and the amount ofpotassium fluoborate being sufficient to dissolve the boron oxide,electrolyzing said mixture in an electrolytic cell having a removableiron cathode to deposit boron on the cathode while adding boron oxideperiodically to replace that consumed by electrolysis, and removing thecathode from the cell from time to time for recovery of boron therefrom,the recovery of boron from the cathode being performed so as to leave anadherent coating of boron substantially completely covering andprotecting the surface of that part of the cathode immersed in the fusedbath.

15. In the process of preparing boron in a carbon lined electrolyticcell by electrolyzing a fused mixture consisting essentially of apotassium salt of a normally gaseous halogen, potassium fluoborate, andboron oxide, the step which comprises skimming carbon containingimpurities from the surface of said fused mixture periodically duringthe process to reduce the carbon content of boron deposited on thecathode.

16. In the process of preparing boron in a carbon lined electrolyticcell by electrolyzing, at a temperature in the range of 650 to 1000 C.,a fused mixture consisting essentially of potassium chloride, potassiumfiuoborate, and boron oxide, the improvement which comprises skimmingcarbon containing impurities from the surface of said fused mixtureperiodically during the process to reduce the carbon content of borondeposited in the cathode.

17. In the process of preparing boron in a carbon lined electrolyticcell by electrolyzing, at a temperature in the range of 800 to 1000 C.,a fused mixture consisting essentially of potassium fluoride, potassiumfiuoborate, and boron oxide, the improvement which comprises skimmingcarbon containing impurities from the surface of said fused mixtureperiodically during the process to reduce the carbon content of borondeposited in the cathode.

18. In the process of preparing boron in a carbon lined electrolyticcell by electrolyzing, at a temperature in the range of 650 to 1000 C.,a fused mixture consisting essentially of potassium chloride, potassiumfluoborate, and boron oxide, while adding boron periodically during theprocess to replace that consumed during the electrolysis, theimprovement which comprises skimming carbon containing impurities fromthe surface of said fused mixture periodically during the process toreduce the carbon content of boron deposited on the cathode.

19. In the process of preparing boron in a carbon lined electrolyticcell by electrolyzing, at a temperature in the range of 800 to 1000 0.,a a fused mixture consisting essentially of potassium fluoride,potassium fluoborate, and boron oxide, while adding boron periodicallyduring the process to replace that consumed during the electrolysis, theimprovement which comprises skimming carbon containing impurities fromthe surface of said fused mixture periodically during the process toreduce the carbon content of boron deposited on the cathode.

20. The process of producing elemental boron of high purity whichcomprises electrolyzing, at a temperature in the range of 650 to 10000., a a carbon lined electrolytic cell having an iron cathode removablysuspended therein, a fused mixture consisting essentially of potassiumchloride, potassium fiuoborate, and boron oxide, periodically skimmingcarbon containing impurities from the surface of the bath during theperiod of electrolysis, and periodically withdrawing the cathode andremoving therefrom the major portion of boron deposited thereon whileleaving an adherent coating of boron over substantially the entiresurface of the cathode upon which boron was deposited.

21. The process of producing elemental boron of high purity whichcomprises electrolyzing, at a temperature in the range of 800 to 10000., a a carbon lined electrolytic cell having an iron cathode removablysuspended therein, a fused mixture consisting essentially of potassiumfluoride, potassium fluoborate, and boron oxide, periodically skimmingcarbon containing impurities from the surface of the bath during theperiod of electrolysis, and periodically withdrawing the cathode andremoving therefrom the major portion of the boron deposited thereonwhile leaving an adherent coating of boron over substantially the entiresurface of the cathode upon which boron was deposited.

HUGH S. COOPER.

REFERENCES CITED 1 1s t American Electrochemca ocie y,

vol. 47 (1925), pages 28 thru 33.

Certificate of Correction Patent N 0. 2,572,249 October 23 1951 HUGH F.COOPER It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows:

Column 14, line 16, before fused strike out 11; lines 27 and 42, for1000 C., a. read 1000 8., in;

and that the said Letters Patent should be read as corrected above, sothat the same may conform to the record of the case in the PatentOfiice.

Signed and sealed this 12th day of February, A. D. 1952.

THOMAS F. MURPHY,

Assistant Commissioner of Patents.

1. THE PROCESS OF PREPARING BORON COMPRISING ELECTROLYZING A FUSED BATHCONSISTING ESSENTIALLY OF A POTASSIUM SALT OF A NORMALLY GASEOUSHALOGEN, POTASSIUM FLUOBORATE, AND BORON OXIDE.